


A Small Temptation

by omegadeanlovesalphacas



Category: Supernatural
Genre: Age Difference, Alpha Castiel (Supernatural), Alpha Castiel/Omega Dean Winchester, Alpha/Beta/Omega Dynamics, Alpha/Omega, Castration, Claiming, Dean tries to seduce Castiel, Doctor!Castiel, Knotting, M/M, Omega Dean, Painful Sex, Rough Sex, Size Difference, Size Kink, Student!Dean, Substitute Teacher Castiel, Underage Dean (13), Underage Sex, a bit of slut shaming, almost noncon at points, castiel has a huge cock, dubcon, hint of medical kink, small!dean
Language: English
Status: Completed
Published: 2017-08-20
Updated: 2017-08-20
Packaged: 2018-12-17 14:54:15
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, Underage
Chapters: 1
Words: 3,402
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11853894
Author URL: https://archiveofourown.org/users/omegadeanlovesalphacas/pseuds/omegadeanlovesalphacas
Summary: Doctor!Castiel is moonlighting as a substitute health teacher when he meets 13 and castrated Dean Winchester. He tries to resist the urge to claim the beautifully petite boy, but the omega just won't leave him alone.





	A Small Temptation

**Author's Note:**

> This is an Alpha/omega kink prompt fill. Expect more porn than plot, and lots of power imbalance between Cas and Dean. Mind the warnings and kinks in the tags.
> 
>  **Warning!** This fic includes **Castration Kink!** If you're not familiar, you can read my explanation here: [omegadeanlovesalphacas.tumblr.com/castrationkink](http://omegadeanlovesalphacas.tumblr.com/castrationkink)

How Castiel became a substitute teacher was rather a long story. The short version is that he was a doctor specializing in reproductive health, and his friend Balthazaar was a pushy school district administrator who needed a substitute for health class. So from time to time, when the regular health teacher was out, Castiel would fill in at one school or the other. He actually was starting to enjoy it, although he would never admit that to Balthazaar.

Today he was subbing at the omega school for the very first time. The school was a middle and high school combination that served exclusively presented omegas, giving their families a safer environment where they’d be less likely to be claimed.

The vice principal escorted Castiel to his class room, giving him a schedule of the day’s classes. “Watch out for Dean Winchester in your third period, he’s a trouble maker,” the woman said. “He’s easy to spot, he was castrated young so he’s much smaller than the other 13 year olds.”

Castiel’s eyebrows raised at the comment, but he tried to disguise his interest with a nod, taking the schedule and thanking the woman. Fortunately she left without taking note of Castiel’s reaction.

The truth was, Castiel had always been rather obsessed with castrated omegas, especially ones who were altered at a young age. They were just so wonderfully petite and effeminate, the lack of testosterone making their body small and delicate. They were usually so much more submissive and obedient, and often much more desperate for a knot, as their little cock alone couldn’t make them come. It was Castiel’s dream to mate one.

There was just one problem, Castiel was tall and broad, and endowed with a rather  _huge_  cock. As a doctor, Castiel knew it wasn’t really a good idea for a tiny omega to take an eleven inch cock, if they weren’t built for it they could be seriously injured. The real trouble was that made the fantasy of a castrated omega all the stronger for Castiel, he desperately wanted to have a tiny omega impaled on his massive cock, just the thought made his cock twitch.

But it could never be, so Castiel put thoughts of the omega aside and focused on his classes. The first two classes went pretty well, his students were well behaved, most of them responding to the presence of a strong alpha with natural obedience.

When third period came around, Castiel told himself not to look for the castrated omega, not to even let his mind drift to the possibilities. He hoped the boy would turn out to be unappealing, so that he wouldn’t be distracted.

But when Castiel saw the small boy walk into the room, he was immediately struck by how stunningly beautiful Dean Winchester was. He had bright green eyes and golden freckles across his face, and his body was the most perfectly petite little thing Castiel had ever seen. He was noticeably smaller than the rest of the class and Castiel guessed he was well under five feet tall.

When Dean walked past Castiel on the way to his seat, he barely came up to the alpha’s chest, and Castiel’s dick fucking  _jumped_  in excitement.

Castiel coughed and quickly took his seat behind his desk, trying to ignore the way Dean stole a glance at him and then ducked his gaze submissively. He ended up having to deliver the whole lesson seated at the desk, as his damn dick couldn’t stop thinking about the boy. Castiel kept waiting for him to act out, as he’d been warned, but the boy was nothing but the perfect picture of attentive obedience and submission throughout the whole class.

When class was finally over, Castiel tried not to look at Dean as the students filed out, but he didn’t miss the way the omega’s eyes glanced at him several times on the way out of the room. When the classroom was finally empty Castiel let out a groan and locked the door, it was lunch period and he desperately needed to jerk off or he was going to be sporting a hard on for the rest of the day.

Castiel felt much better by the time fourth period started, and by the end of the day he’d almost been able to get the thoughts of Dean out of his mind. He had one more duty for the day, he’d volunteered to cover detention. It was in another room, so he crossed the school and let himself into what was the history room during the day. He’d been told he only had one kid, so it shouldn’t be too hard.

He stopped dead in his tracks when he saw Dean fucking Winchester sitting in one of the seats, looking sulky. That was until he noticed Castiel walk into the room, at which point the omega brightened and sat up straight, stealing a glance before ducking his eyes again.

Castiel internally groaned, and moved to sit at the desk. “I’m sure you know the rules, sit quietly and do your homework,” he said, hoping he’d survive the hour alone with the beautiful boy.

“Yes, Sir,” Dean said softly, and his voice was smooth and soft.

Castiel’s cock leapt to life at hearing those words come from the boy’s lips, and he was quickly hard again, so very eager for what it saw as a perfect mate. The alpha let out a small growl of frustration and pulled out a book, hoping to distract himself.

The room was silent for a few minutes, and Castiel did his very best to read, but it was hard to focus when he could easily smell the omega’s scent now that it had no other competition in the room. It was intoxicating, even across the room Castiel could tell that the boy was fertile and compatible, an ideal mate. He could even smell a little slick, indicating the omega’s body was responding in kind, whether or not Dean understood it he didn’t know.

“Excuse me, Dr. Novak,” Dean said, interrupting the stillness of the room. “May I please ask you a question?”

Castiel really wanted to tell him no, as just the sound of the boy’s voice was putting him on edge, but he let curiosity get the better of him. “Sure,” he finally said.

Dean bit his lip and nervously tugged that the tall white collar that protected his neck from a claiming bite. “You said you’re a reproductive health doctor, right?” he asked.

“Yes, that’s right,” Castiel said, trying not to stare at the little lock that secured Dean’s collar on his neck. It looked small and like it might be easy to break.

Dean nodded. “So um, you see, I’m castrated,” he said, his face blooming with a pretty blush. “Have been ever since my parents found out I was gonna be an omega,” he said, squirming a little in his seat. “They say it means they can get a better mate for me, that it makes me more desirable.”

Castiel agreed with Dean’s parents, it definitely made the boy more desirable. “Do you have a question about your castration?” he asked, trying to go into doctor mode.

Dean was still blushing. “Yeah, um, I was wondering…” He looked up at Castiel and then down at his hands again. “Can castrated omegas still get pregnant?”

Castiel’s eyebrows rose. “Yes, of course they can Dean.”

Dean looked a little relieved at that, but still concerned. “Oh. Okay, good.” He gave Castiel a little smile. “All I want is to be a good mate for my future Alpha and carry his pups. I just want to know that I’m normal, that an Alpha won’t reject me.”

“I can smell the scent of your fertility from here, Dean,” Castiel admitted. “I don’t think you’ll have any problem bearing pups.”

Dean smiled at Castiel. “Thank you.” He bit his lip and looked at his lap. “There’s one other thing…”

“Yes?” Castiel asked, desperately hoping this conversation would end soon and he would be able to get away from the horrible temptation that was Dean Winchester.

“Since you’re a doctor, could you just take a look and tell me if I’m normal, for a castrated omega?” Dean asked, not making eye contact with Castiel. “I’m just so… small.” His cheeks were a beautiful pink again.

Castiel’s cock ached when he realized the boy meant his dick was small. God Castiel loved the look of a little omega cock after castration, he really should say no. “Of course,” he heard himself say.

Dean jumped up and approached the desk, coming around behind it to stand next to Castiel’s chair. He looked nervously at the alpha. “Should I take off my pants?”

“Close the door and lock it first,” Castiel heard himself saying. “Then strip down for me please.” His cock throbbed as he watched Dean hurry to comply, and he wondered if the boy had noticed the bulge in his slacks, now that the alpha couldn’t hide behind the desk anymore.

Dean quickly closed the door and locked it before returning to stand in front of Castiel. He quickly unbuttoned his jeans and pushed them down, taking his underwear with them. His little cock was left exposed to the alpha, surrounded by smooth and hairless skin, another lovely trait of castrated omegas.

“Looks perfectly normal,” Castiel said, his desire starting to get the better of him. “Would you like me to examine you, Dean? So we can make sure everything is okay?”

Dean blushed and nodded. “Yes, please.”

Castiel’s hands reached out of it’s own accord, he could no longer stop himself from touching. One hand rested on Dean’s hip, while the other reached out to run a teasing fingertip over the small cock, watching the way it twitched.

Dean let out a little whimper, but didn’t stop Castiel. “Is that normal?”

Castiel nodded, continuing to tease the cute little cock, brushing it with his fingers before gently grasping it and tugging. “Castrated omegas usually can’t quite get fully hard, you should be enjoying this, but it wouldn’t be able to give you an orgasm. Does it feel good, Dean?”

Dean moaned and nodded. “Y-yes, it feels good.”

Castiel noticed a little more slick was escaping and running down the inside of Dean’s leg. “Slick production looks normal,” he said with a chuckle. “Let’s take a look.” He gently spun the boy around using his strong hands on his hips, and Dean moved willingly. “Bend over and spread your legs for me, Dean.”

Dean did as he was told, offering his slick entrance to the alpha’s greedy gaze. “Does it look okay?”

“It looks perfect,” Castiel said, his hands caressing the round swell of Dean’s ass, his thumb finding the puckered hole and circling it before pressing inside.

Dean gasped and pushed back on the finger. “Oh, Alpha, please!”

Castiel realized he was taking this way too far, and he quickly removed his hands from the tempting boy. “You’re perfectly normal Dean, and fully fertile. Please pull up your pants and return to your desk.”

Dean looked crestfallen as he stood and pulled up his pants, but he nodded and gave Castiel a quiet “Yes, Sir” before going back to his desk.

Castiel watched as the boy took his seat, looking quite dejected as he turned his attention back to his homework. Castiel tried not to think about the opportunity he’d just refused as he went back to his book. His cock throbbed, furious in it’s neglect.

The rest of the hour passed with tense silence, the scent of mutual arousal hanging in the air. When the bell finally rang, Castiel let out a long breath, eager to remove himself from the worst temptation he’d ever known.

He watched as Dean stood and and slowly gathered his things, and Castiel stood and headed for the door, ready to leave. “Goodbye Mr. Winchester,” he said, turning to let the omega pass him so he could lock up behind.

Dean slowly moved to leave, and as he made to pass Castiel his eyes dropped to the still sizable bulge in the front of the alpha’s pants.

Suddenly the omega’s hand shot out and ran down the length of Castiel’s cock where it tented his slacks, and the alpha gasped at the sudden flair of pleasure.

“What the hell are you doing?” Castiel snapped, snatching Dean’s wrist in his hand and pulling it away.

Dean yelped a little when the alpha grabbed him, but he only went after Castiel’s dick again, this time with his other hand. “Please Alpha, I just want to see it!” he begged. “I’m supposed to take an alpha’s cock someday, I just want to know how big they are!”

Castiel’s whole body shook with the effort of holding himself back, and he could feel his control slipping. “Then take it out,” he growled, immediately knowing that was a mistake but unable to stop the words from escaping. He let go of Dean’s wrist, trying to tell himself he was just going to satisfy the boy’s curiosity and send him on his way.

Dean eagerly tugged down the zipper of Castiel’s slacks and started to work the alpha’s dick free, and his eyes went wide when the massive cock emerged. A moan escaped Castiel’s lips when he felt the gentle touch of the omega’s hands on his length, gently stroking.

“Oh wow,” Dean breathed, feeling the weight in his hands. “You’re so big! Are all alphas as big as you, Dr. Novak?”

“No, I’m well above average,” Castiel growled, clenching his fists as he fought to restrain himself. “You’ve had your look, now put it away.”

Dean’s face fell. “Oh, but please Alpha, I want to know more!” he begged, still gently stroking Castiel’s cock.

“What more could you possibly want to know?” Castiel snapped.

“Well…” Dean shifted nervously, looking up at Castiel with bashful eyes. “You see, sometimes I let the older omegas fuck me. And it feels nice and all, but they’re so much smaller than you, and I just really want to know what a real alpha knot feels like. Please, Alpha?” He leaned in closer, letting Castiel’s straining cock press against his belly.

That was finally as much as Castiel could take, and he snapped and grabbed Dean, spinning him around and picking him up in one smooth motion, laying him out on his back on the desk.

“You want to be fucked by an alpha?” Castiel growled, yanking Dean’s shirt over his head before moving to his pants. He wanted the boy naked,  _now._ “Fine. I’ll make sure you never want an omega dick in that greedy hole ever again, make sure nothing short of a massive alpha knot will ever be enough!”

Dean whimpered as he was roughly stripped naked, and he grabbed for Castiel. “Yes, yes, please!”

Once he finally had Dean sprawled out naked, Castiel pushed the omega’s knees up and spread them open, admiring the way his little hole winked and leaked slick. He knew he should prep the boy, but he wanted to teach him a lesson, punish him for being such a little slut. So with an excited growl he lined his massive cock up to Dean’s little hole and thrust, forcing the head past the tight ring of muscle. Dean cried out in pain as Castiel’s hips snapped, driving his cock in deeper, and  _oh god_  he’s  _so tight!_  It’s the best thing Castiel had ever felt, and he thrust in harder, determined to fill the omega to the hilt.

“Stop!” Dean cried out, whimpering in pain. “It’s too big, I can’t!”

Castiel just growled, gripping Dean’s hips and slamming in harder. “Take it!” he snapped. “You wanted to get fucked by an alpha, so be a good bitch and take it!” He couldn’t stop himself, he finally had the most perfect little omega impaled on his cock and he was determined toknot him.

Dean stopped begging, submitting to Castiel. But he continued to whimper and moan, writhing on the table in an overwhelming mix of pain and pleasure. “So big, so big, oh god!” he gasped out, eyes wet with tears.

Castiel snarled as he slammed in harder, driving in the last few inches until his heavy balls finally slapped against Dean’s ass and his massive cock was blissfully fully seated inside the little omega. He stilled for a moment to enjoy it before he started to move again, hips snapping as he thrust deep inside Dean.

Castiel looked down at the tiny omega squirming on his cock, and he was startled to see a small bump appear on the omega’s belly each time he drove into the boy. He reached out to touch it and realized he was touching his own cock, and he let out a long moan at the implication. He drew his cock back and thrust in hard again, groaning as he felt the pressure of his hand from inside Dean.

Dean was shaking and moaning as Castiel leaned down to cover the small boy with his body, picking up his pace and fucking him harder. “This is going to seem like nothing in a minute,” he said into Dean’s ear. “You still have to take my knot.”

“I can’t, I can’t!” Dean whined, shaking his head back and forth, panting and moaning with each thrust. “It’s too big!”

“You can,” Castiel growled, his knot swelling as he intentionally pushed in and out of the omega, feeling the boy’s tight rim stretch around him. “Your body was made for this.” He watched as each thrust made the omega’s belly bulge with the fullness of his cock.

Dean just whimpered as Castiel continued to fuck him, knot growing until the omega started to shake with pleasure. With a snap of his hips, Castiel slammed his knot deep into Dean, and the omega suddenly came hard as the alpha continued to drive into him. Castiel groaned when he realized the omega orgasmed dry, yet another thing he loved about castrated omegas.

With his orgasm, Dean’s channel gripped tightly around Castiel’s knot, and the alpha let out a long moan. “Fuck,” he growled, reaching down to grab the omega’s little cock. He started to stroke it, extending Dean’s orgasm so that he’d continue to squeeze and ripple around his swelling knot.

“No, it’s too much!” Dean gasped out, trying to push Castiel’s hands away from his cock.  He let out a long moan, tears running from his eyes, overwhelmed by the overstimulation.

“Stop complaining,” Castiel snapped, grabbing Dean’s wrists in one hand and pinning them above his head. “This is just what little sluts like you deserve,” he said, hips snapping as he drove in harder, his other hand still tugging on Dean’s cock. “You should have known that when you decided to seduce your teacher.”

Dean cried and moaned as his orgasm was stretched out torturously long, and Castiel tried to hold back for a few more moments, but he finally lost control and slammed into Dean with a long groan. He came hard, his knot tying inside the omega and his seed filling him, and he slumped against the exhausted omega.

Without thinking twice, Castiel’s hand grabbed the lock on Dean’s collar, snapping it off with a sharp twist of his wrist. In another moment he had the collar off the omega’s neck and his teeth sunk deep into the bared neck of his new mate.

Finally satisfied, Castiel sat up, looking down at his omega. He was naked, knotted, and marked, and the alpha watched as his belly pulsed and swelled as his knot steadily bred him full. His eyes were closed, exhausted and breathing hard. It was the best thing he’d ever seen.

Castiel smiled, reaching out to stroke Dean’s belly. “You’re all mine, now. Mine to use as I please. You’re going to be filled up like this every day, morning and night.” He reached out to run his hand through Dean’s hair, gripping gently. “I’m going to force my cock down your throat every morning so you can suck down your breakfast, that’s what little sluts like you deserve,” he said, hips moving a little as his knot continued to fill the omega.

Dean let out a little moan, opening his eyes, looking up at Castiel with a small smile.

“Promise?”

**Author's Note:**

> Thanks for reading, I hope you enjoyed it. Comments are love! <3
> 
> Visit me on Tumblr: [omegadeanlovesalphacas.tumblr.com/mobilemenu](http://omegadeanlovesalphacas.tumblr.com/mobilemenu)


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